Is there a workaround for error: "Could not write image: Too many open files"?
The workaroud that I have developed is as follows. 


Render my scene.
View>Toggle Fullscreen Area
View>View Fit
Zoom in to a level where the pixels in the image are larger than the pixels of your display. 
Take screen captures of each part of the image. (On Windows, Shipping Tool works well)
Stitch these together in an image editing software. I used Photomerge in Photoshop Elements.
Remove the border using a pixel color select tool and crop (in Photoshop Elements, the magic wand works well)
Resize your image to the original desired resolution. This is also an opportunity to touch up those nasty fireflies.
Save and share. 


I hope this helps.